认识“环境敏感型”生物大分子

生物技术在现代生活中扮演着越来越重要的角色。本文着重分析了＂环境敏感型＂大分子及大分子体系在特定环境条件下发生的一些特定的物理和化学性质的变化机理以及利用控制大分子构象得到对特定外界因素敏感的大分子或大分子体系。目的是认识＂环境敏感型＂大分子或大分子体系在生物技术产品的分离纯化上的具体应用。     

Selective Pharmacophore Models of Dopamine D1 and D2 Full Agonists Based on Extended Pharmacophore Features

This study is focused on the identification of structural features that determine the selectivity of dopamine receptor agonists toward D₁ and D₂ receptors. Selective pharmacophore models were developed for both receptors. The models were built by using projected pharmacophoric features that represent the main agonist interaction sites in the receptor (the Ser residues in TM5 and the Asp in TM3), a directional aromatic feature in the ligand, a feature with large positional tolerance representing the positively charged nitrogen in the ligand, and sets of excluded volumes reflecting the shapes of the receptors. The sets of D₁ and D₂ ligands used for modeling were carefully selected from published sources and consist of structurally diverse, conformationally rigid full agonists as active ligands together with structurally related inactives. The robustness of the models in discriminating actives from inactives was tested against four ensembles of conformations generated by using different established methods and different force fields. The reasons for the selectivity can be attributed to both geometrical differences in the arrangement of the features, e.g., different tilt angels of the π system, as well as shape differences covered by the different sets of excluded volumes. This work provides useful information for the design of new D₁ and D₂ agonists and also for comparative homology modeling of D₁ and D₂ receptors. The approach is general and could therefore be applied to other ligand–protein interactions for which no experimental protein structure is available.     

Self-Assembly of Poly(Amino Acid)s Mediated by Secondary Conformations

Self-assembly of block copolymers has recently drawn great attention due to its remarkable performance and wide variety of applications in biomedicine, biomaterials, microelectronics, photoelectric materials, catalysts, etc. Poly(amino acid)s (PAAs), formed by introducing synthetic amino acids into copolymer backbones, are able to fold into different secondary conformations when compared with traditional amphiphilic copolymers. Apart from changing the chemical composition and degree of polymerization of copolymers, the self-assembly behaviors of PAAs could be controlled by their secondary conformations, which are more flexible and adjustable for fine structure tailoring. In this article, we summarize the latest findings on the variables that influence secondary conformations, in particular the regulation of order-to-order conformational changes and the approaches used to manage the self-assembly behaviors of PAAs. These strategies include controlling pH, redox reactions, coordination, light, temperature, and so on. Hopefully, we can provide valuable perspectives that will be useful for the future development and use of synthetic PAAs.     

冠醚结构新探

文章对冠醚配合物和冠醚结构提出了新的认识,认为配合物的空间构型应该由中心原子杂化轨道的类型来决定,由此可推出冠醚配合物的结构一般应该是立体的。冠醚中σ键的柔顺性使其氧原子的位置有可能与中心原子的杂化轨道相匹配。从合成冠醚的模板效应以及多苯并冠醚与金属离子生成的配合物稳定性降低,可以得到冠醚配合物不是平面环形配位的佐证。文中讨论了直径匹配和配位数匹配,并对负离子(或水)参与配位进行了解释。文章指出,冠醚的稳定构象既不是王冠式,也不是汽车轮胎式,而应该是交叉式。交叉式构象中,氧原子的位置正好能与金属离子的杂化轨道相匹配,对冠醚结构的新认识,为拓宽冠醚的应用提供了依据。     

Micellar solutions of amphipathic copolymers based on carboxymethyl cellulose

A novel family of amphipathic copolymers based on carboxymethyl cellulose (CM‐cellulose) has been synthesized through ultrasonic irradiation. Their micellar conformation in aqueous solution was studied by dynamic laser scattering, environmental scanning electron microscopy and gel permeation chromatography. The results show that conformation of copolymer molecules is totally different from that of CM‐cellulose because of the introduction of the surface active macromonomers. Due to the influence of hydrophobic character and molecular weight, different amphipathic copolymers have different micellar conformations, such as cylindrical, spheroidal or ellipsoidal micelles. In the range of concentration tested, the normalized first‐order autocorrelation function g⁽¹⁾(τ) of a copolymer of CM‐cellulose and poly(ethylene oxide) dodecyl ether acrylate does not fit a single‐exponential decay, indicating a polydisperse system and the existence of species of different shapes and size. At different concentrations, the hydrodynamic radii of micelles (R) almost distribute into two regions of smaller and larger size. With increasing copolymer concentration, the region of smaller R remains in the range 30–100 nm and is considered to represent monomolecular micelles, while the larger R region increases gradually with concentration, which means that polymolecular micelles increase in size. © 2003 Society of Chemical Industry     

准噶尔盆地白家海凸起油气成藏的关键因素

白家海凸起是夹持于三大生油凹陷的一个形成较早继承性古隆起,在整个油气运移的过程中始终处于有利的运移通道上,它控制着油气的平面运移效应。多年的勘探证实,白家海凸起主要的油气藏类型为构造油气藏,地层油气藏及地层—岩性油气藏形成的规模较小,而且主要位于白垩系与侏罗系不整合面附近的中上侏罗统。因此,白家海凸起的勘探应以寻找构造圈闭为主要任务。     

Characterization of α-carrageenan solution behavior by field-flow fractionation and multiangle light scattering

The salt mediated molecular conformation change of alpha (α)-carrageenan was studied in 0.1 M solutions of NaCl, NaI, and KCl. Asymmetric Field-Flow Fractionation with multiangle laser light scattering (AFFF/MALLS) detection was used to determine the average molecular weight, radius of gyration, and hydrodynamic radius which were in turn used to calculate the molecular density. In the presence of 0.1 M NaCl, an inert salt that does not promote gelation, α-carrageenan has a denser structure compared to κ-carrageenan of a similar molecular weight. A distinct and dramatic increase in the molecular weight (factor of 2) was observed for α-carrageenan in 0.1 M NaI compared to 0.1 M NaCl. This combined with only a slight change in the radius of gyration, suggests intermolecular interaction to a more compact structure (e.g., coaxial helices). A similar increase in molecular weight is observed in 0.1 M KCl, accompanied with an approximate 50% increase in the radius of gyration as well as an increase in polydispersity. This may also be attributed to intermolecular interaction with helix formation (coaxial or lateral) or may be due to K⁺ cations interacting with naturally occurring residual ι-carrageenan in the sample. As previously reported for other carrageenans the random coil to helix transition of α-carrageenan appears to be stabilized by K⁺ cation or I⁻ anion in an aqueous environment.     

城市地铁盾构法区间隧道的设计

广州地铁二号线越秀公园一三元里区间盾构隧道已于2002年建成并投入试运营。阐述了该隧道的设计概况，主要内容包括：盾构隧道的线路拟合，衬砌环的构造形式，管片的结构设计和结构防水。总结了广州盾构隧道设计中的成功经验，并对当前盾构隧道设计中有关问题提出了建议。